1. Field
The following description relates to subsurface exploration, and more particularly, to an apparatus and method for imaging a subsurface using frequency-domain elastic reverse-time migration.
2. Description of the Related Art
Subsurface exploration has been used to discover the subsurface and geological characteristics of a specific region, and particularly, to find natural resources such as oil buried in the subsurface. With an increase in use amount of underground resources, subsurface exploration has been widely performed on sea, as well as on the earth surface. Subsurface exploration on the earth or sea plays an important role in finding fossil fuel, such as natural gas or oil, which is important energy sources, or in understanding a subsurface structure, detecting groundwater, etc.
A subsurface imaging technique is the most important part in subsurface exploration technology. Since acquisition of accurate subsurface images results in an accurate location selection for oil drilling, the subsurface imaging technique will contribute to a significant increase of the success probability of oilfield field development. Recently, due to an increase of demands for oil and gas resources and oil price hikes over the world, a concern to development of oil fields in deep sea bottoms and complicated topography, whose development has been delayed due to financing problems, is increasing. Since development of oil fields in deep sea bottoms and complicated topography requires higher costs compared to development of oil fields in sedimentary topography, a more improved subsurface imaging technique is needed.
Subsurface imaging techniques in acoustic medium have made a huge breakthrough. For example, in the subsurface imaging techniques in acoustic medium, various imaging techniques, such as an imaging technique based on the Kirchoff migration using a travel time curve, a subsurface imaging technique based beam migration, a subsurface imaging technique based on uni-directional or bi-directional wave equation, etc., have been proposed and developed. An imaging technique in acoustic medium is based on an imaging condition suggested by Professor Claerbout, which is a method of acquiring a location for imaging using a correlation between forward modeling data and backward modeling data.
A location for imaging of Acoustic medium can be relatively easily acquired since acoustic medium has only the P-wave component. However, since elastic medium has all of P, S and Rayleigh waves, it is not easy to obtain a location for imaging since undesired artifacts may be produced due to a correlation between the P, S and Rayleigh waves. In order to overcome the problem of elastic medium, studies into a method of applying the Helmholtz decomposition theorem to divide modeling data given as displacements into P- and S-wave potentials to thereby achieve imaging have been conducted. However, since the method is applied only to the time domain, and imaging of elastic medium requires a great deal of computer memory and computing time compared to acoustic medium, the method has difficulties in imaging wide regions.